Here is a simplification of the issue...let's suppose your next door neighbor had a son that, for whatever reason, was thrown out of his house. Out of the kindness of your heart, you allow him to live in your house until he can go home.
Eventually he gets so comfortable in your house (because he has many more rights and freedoms there) that he decides that your house is his house.
Now he wants his friends and family to enjoy the same rights and freedoms he has, so he tries to get them to move in to your house. When you explain to him that you don't have room for all these people, he tells you that he will kill you and your family members so that his "people" can take over your home.
(In case you were wondering, your home represents Israel, and your neighbor represents the "palestinians".)